This study is designed to discover and develop new radioligands to be used for neuroimaging by single photon emission computerized tomography (SPECT) and positron emission tomography (PET). We have developed a rapid radioiodination method for labeling Schering-Plough's D-1 antagonist SCH-23390 ("FISCH"), and are presently involved in a collaborative effort with NIDDK to develop ligands for sigma receptors and for dopamine uptake. Several compounds have been synthesized and are currently being evaluated for their potential use as neuroimaging agents. A compound developed in this laboratory for the purpose of imaging dopamine uptake, N-(4-iodobenzyl)imipramine, lacked potential due to the limited solubility of the free base or any of its salts in aqueous media. We are now focused primarily on the synthesis and evaluation of several compounds targeted for the N-methyl-D-aspartate subclass of glutamate receptors. Current "production line" projects involve radioiodination of IQNB (muscarinic receptor ligand) and IBZM (D-2 ligand) for use in patient studies.